Electromagnetic bandgap structure and printed circuit board

ABSTRACT

Disclosed are an electromagnetic bandgap structure and a printed circuit board that can solve a mixed signal problem between an analog circuit and a digital circuit. The electromagnetic bandgap structure in which a first metal layer, a first dielectric layer, a second dielectric layer and a second metal layer are stacked can include a first metal plate, formed between the first dielectric layer and the second dielectric layer; a second metal plate, formed on a same planar surface as the first metal plate, accommodated into a hole which is formed in the first metal plate and electrically connected to the first metal plate through a metal line; and a via, connecting the second metal plate to any one of the first metal layer and the second metal layer. With the present invention, the electromagnetic bandgap structure can be not only miniaturized but also have a low bandgap frequency.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of Korean Patent Application Nos.10-2007-0010364, filed on Feb. 1, 2007 and 10-2007-0093956, filed onSep. 17, 2007, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board, morespecifically to a printed circuit board that can solve a mixed signalproblem between an analog circuit and a digital circuit.

2. Background Art

Various apparatuses such as mobile communication terminals, personaldigital assistants (PDA), laptop computers and digital multimediabroadcasting (DMB) devices have been launched in order to meet today'strend that mobility is considered as one of the most important issues.

Such apparatuses include a printed circuit board, which is configured tocompound analog circuits (e.g. radio frequency (RF) circuits) anddigital circuits for wireless communication.

FIG. 1 is a sectional view showing a printed circuit board including ananalog circuit and a digital circuit. Although a 4-layered printedcircuit board is illustrated, various printed circuit boards such as 2and 6-layered printed circuit boards can be applied. Here, the analogcircuit is assumed to be an RF circuit.

The printed circuit board 100 includes metal layers 110-1, 110-2, 110-3and 110-4 (hereinafter, collectively referred to as 110), dielectriclayers 120-1, 120-2 and 120-3 (hereinafter, collectively referred to as120) stacked in between the metal layers 110, a digital circuit 130mounted on the top metal layer 110-1 and an RF circuit 140.

If it is assumed that the metal layer 110-2 is a ground layer and themetal layer 110-3 is a power layer, a current passes through a via 160connected between the ground layer 110-2 and the power layer 110-3 andthe printed circuit board 100 performs a predetermined operation orfunction.

Here, an operation frequency of the digital circuit 130 and anelectromagnetic (EM) wave 150 by harmonics components are transferred tothe RF circuit 140, to thereby generate a problem mixed signals. Themixed signal problem is generated due to the EM wave, having a frequencywithin the frequency band in which the RF circuit 140 is operated, inthe digital circuit 130. This problem results in obstructing theaccurate operation of the RF circuit 140. For example, when the RFcircuit 140 receives a signal ranging a certain frequency band,transferring the EM wave 150 including the signals ranging the certainfrequency band from the digital circuit 130 may make it difficult toaccurately receive the signal ranging the certain frequency band.

Solving the mixed signal problem becomes more difficult due to theincreased complexity of electronic apparatuses and the higher operationfrequency of the digital circuit 130.

The decoupling capacitor method, which is a typical solution for powernoise, is not adequate for high frequencies. Accordingly, it isnecessary to intercept or decrease the noise of the high frequenciesbetween the RF circuit 140 and the digital circuit 130.

FIG. 2 is a sectional view showing an electromagnetic bandgap structurethat solves a problem mixed signals between an analog circuit and adigital circuit in accordance with a conventional art, and FIG. 3 is aplan view showing a metal plate configuration of the electromagneticbandgap structure shown in FIG. 2. FIG. 4 is a perspective view showingthe electromagnetic bandgap structure shown in FIG. 2, and FIG. 5 is aschematic view showing an equivalent circuit of the electromagneticbandgap structure shown in FIG. 2.

The electromagnetic bandgap structure 200 includes a first metal layer210-1, a second metal layer 210-2, a first dielectric layer 220 a asecond dielectric layer 220 b, a meal plate 232 and a via 234.

The first metal layer 210-1 and the metal plate 232 are connected toeach other through the via 234. A mushroom type structure 230 is formedto include the metal plate 232 and the via 234 (refer to FIG. 4).

If the first meal layer 210-1 is a ground layer, the second metal layer210-2 is a power layer. Also, if the first metal 210-1 is the powerlayer, the second layer 210-2 is the ground layer.

In other words, the repeated formation of the mushroom type structure230 (refer to FIG. 3) results in a bandgap structure preventing a signalhaving a certain frequency band from being penetrated. At this time, themushroom type structures 230, including the metal plates 232 and thevias 234, are repeatedly formed between the ground layer and the powerlayer.

The function preventing a signal having a certain frequency band frombeing penetrated, which is based on resistance R_(E) and R_(P),inductance L_(E) and L_(P), capacitance C_(E), C_(P) and C_(G) andconductance G_(P) and G_(E), is approximated to the equivalent circuitshown in FIG. 5.

A mobile communication terminal is a good example for an electronicapparatus employing the board realized with the digital circuit and theRF circuit together. In the case of the mobile communication terminal,solving the problem mixed signals needs the noise shielding of anoperation frequency band of the RF circuit between 0.8 and 2.0 GHz. Thesmall sized mushroom type structure is also required. However, theforegoing electromagnetic bandgap structure may not satisfy the twoconditions needed to solve the problem mixed signals.

The reduced size of the mushroom type structure results in the increaseof the bandgap frequency to block pertinent noise, to thereby bringabout inefficient operation in the frequency band of 0.8 to 2.0 GHz,which is the operation frequency band of the RF circuit in the foresaidmobile communication terminal.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an electromagnetic bandgapstructure and a printed circuit board that can be not only miniaturizedbut also have a low bandgap frequency.

The present invention also provides an electromagnetic bandgap structureand a printed circuit board that can solve a problem mixed signals in anelectronic apparatus (e.g. a mobile communication terminal) employingthe board having the digital circuit and the RF circuit, realizedtherein together.

The present invention provides an electromagnetic bandgap structure anda printed circuit board that can allow the noise of a particularfrequency not to be penetrated.

An aspect of present invention features an electromagnetic bandgapstructure that can prevent a signal having a frequency band from beingtransferred.

According to an embodiment of the present invention, the electromagneticbandgap structure in which a first metal layer, a dielectric layer, asecond dielectric layer and a second metal layer are stacked can includea first metal plate, formed between the first dielectric layer and thesecond dielectric layer; a second metal plate, formed on a same planarsurface as the first metal plate, accommodated into a hole which isformed in the first metal plate and electrically connected to the firstmetal plate through a metal line; and a via, connecting the second metalplate to any one of the first metal layer and the second metal layer.

Here, the metal line can be formed on a same planar surface as the firstmetal plate and the second metal plate.

Also, the first metal plate can be away from the second metal plate at apredetermined interval.

The metal line can have a straight-line shape or a curved shape.Alternatively, the metal line can have a spiral shape enveloping thesecond metal plate.

According to another embodiment of the present invention, anelectromagnetic bandgap structure can include a first metal layer; afirst dielectric layer, stacked in the first metal layer; a metal plate,stacked in the first dielectric layer; a via, having one end part whichis connected to the first metal layer; a second dielectric layer,stacked in the metal plate and the first dielectric layer; and a secondmetal layer, stacked in the second dielectric layer. Here, the other endpart of the via can be connected to a via land which is placed in a holeformed in the metal plate, and the via land can be connected to themetal plate through a metal line.

Another aspect of present invention features a printed circuit boardthat can prevent a signal having a frequency band from being transferredby having an analog circuit and a digital circuit.

According to an embodiment of the present invention, a printed circuitboard can include an electromagnetic bandgap structure which is disposedbetween the analog circuit and the digital circuit, the electromagneticbandgap structure including a first metal plate, formed between thefirst dielectric layer and the second dielectric layer; a second metalplate, formed on a same planar surface as the first metal plate,accommodated into a hole which is formed in the first metal plate andelectrically connected to the first metal plate through a metal line;and a via, connecting the second metal plate to any one of the firstmetal layer and the second metal layer.

Here, the first metal layer can be any one of a ground layer and a powerlayer, and the second metal layer can be the other.

The analog circuit can be an RF circuit including an antenna receiving awireless signal from an outside.

The metal line can be formed on a same planar surface as the first metalplate and the second metal plate.

Also, the first metal plate can be away from the second metal plate in apredetermined interval.

The metal line can have a straight-line shape or a curved shape.Alternatively, the metal line can have a spiral shape enveloping thesecond metal plate.

A plurality of electromagnetic bandgap structures can be arrangedbetween the analog circuit and the digital circuit.

According to an embodiment of the present invention, the printed circuitboard can include an electromagnetic bandgap structure which is disposedbetween the analog circuit and the digital circuit, the electromagneticbandgap structure including a first metal layer; a first dielectriclayer, stacked in the first metal layer; a metal plate, stacked in thefirst dielectric layer; a via, having one end part which is connected tothe first metal layer; a second dielectric layer, stacked in the metalplate and the first dielectric layer; and a second metal layer, stackedin the second dielectric layer. Here, the other end part of the via canbe connected to a via land which is placed in a hole formed in the metalplate, and the via land can be connected to the metal plate through ametal line.

The first metal layer can be any one of a ground layer and a powerlayer, and the second metal layer is the other. The analog circuit canbe an RF circuit including an antenna receiving a wireless signal froman outside. The metal line can have a straight-line shape, a curvedshape or a spiral shape

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended Claims and accompanying drawings where:

FIG. 1 is a sectional view showing a printed circuit board includinganalog circuit and a digital circuit;

FIG. 2 is a sectional view showing an electromagnetic bandgap structurethat solves a problem mixed signals between an analog circuit and adigital circuit in accordance with a conventional art;

FIG. 3 is a plan view showing a metal plate configuration of theelectromagnetic bandgap structure shown in FIG. 2;

FIG. 4 is a perspective view showing the electromagnetic bandgapstructure shown in FIG. 2;

FIG. 5 is a schematic view showing an equivalent circuit of theelectromagnetic bandgap structure shown in FIG. 2;

FIG. 6 is a sectional view showing an electromagnetic bandgap structurewhich solves a mixed signal problem between an analog circuit and adigital circuit;

FIG. 7 is a plan view metal plate configuration of the electromagneticbandgap structure according to the A-A′ line of FIG. 6;

FIG. 8 is a perspective view showing the electromagnetic bandgapstructure shown in FIG. 6;

FIG. 9 is graphs showing results that are computer-simulated by usingelectromagnetic bandgap structures in accordance with a conventional artand an embodiment of the present invention;

FIG. 10 is a 3-D perspective view showing an electromagnetic bandgapstructure in accordance with another embodiment of the presentinvention;

FIG. 11 is a plan view showing the structure in which a plurality ofmetal plates of the electromagnetic bandgap structure shown in FIG. 10are arranged;

FIG. 12 is a 3-D perspective view showing an electromagnetic bandgapstructure in accordance with another embodiment of the presentinvention;

FIG. 13 is a plan view showing the structure in which a plurality ofmetal plates of the electromagnetic bandgap structure shown in FIG. 12are arranged;

FIG. 14 is graphs showing results that are computer-simulated by usingelectromagnetic bandgap structures in accordance with a conventional artand another embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Since there can be a variety of permutations and embodiments of thepresent invention, certain embodiments will be illustrated and describedwith reference to the accompanying drawings. This, however, is by nomeans to restrict the present invention to certain embodiments, andshall be construed as including all permutations, equivalents andsubstitutes covered by the spirit and scope of the present invention.Throughout the drawings, similar elements are given similar referencenumerals. Throughout the description of the present invention, whendescribing a certain technology is determined to evade the point of thepresent invention, the pertinent detailed description will be omitted.

Terms such as “first” and “second” can be used in describing variouselements, but the above elements shall not be restricted to the aboveterms. The above terms are used only to distinguish one element from theother. For instance, the first element can be named the second element,and vice versa, without departing the scope of claims of the presentinvention. The term “and/or” shall include the combination of aplurality of listed items or any of the plurality of listed items.

When one element is described as being “connected” or “accessed” toanother element, it shall be construed as being connected or accessed tothe other element directly but also as-possibly having another elementin between. On the other hand, if one element is described as being“directly connected” or “directly accessed” to another element, it shallbe construed that there is no other element in between.

The terms used in the description are intended to describe certainembodiments only, and shall by no means restrict the present invention.Unless clearly used otherwise, expressions in the singular numberinclude a plural meaning. In the present description, an expression suchas “comprising” or “consisting of” is intended to designate acharacteristic, a number, a step, an operation, an element, a part orcombinations thereof, and shall not be construed to preclude anypresence or possibility of one or more other characteristics, numbers,steps, operations, elements, parts or combinations thereof.

Unless otherwise defined, all terms, including technical terms andscientific terms, used herein have the same meaning as how they aregenerally understood by those of ordinary skill in the art to which theinvention pertains. Any term that is defined in a general dictionaryshall be construed to have the same meaning in the context of therelevant art, and, unless otherwise defined explicitly, shall not beinterpreted to have an idealistic or excessively formalistic meaning.

Hereinafter, some embodiments of the present invention will be describedin detail with reference to the accompanying drawings.

FIG. 6 is a sectional view showing an electromagnetic bandgap structurewhich solves a mixed signal problem between an analog circuit and adigital circuit, and FIG. 7 is a plan view metal plate configuration ofthe electromagnetic bandgap structure according to the A-A′ line of FIG.6. FIG. 8 is a perspective view showing the electromagnetic bandgapstructure shown in FIG. 6.

In FIG. 6 are illustrated the sectional view showing the electromagneticbandgap structure 300 including a first metal layer 210-1, a secondmetal layer 210-2, a first dielectric layer 220 a, a second dielectriclayer 220 b, a metal plate 332 and a via 334.

The first metal layer 210-1 and the metal plate 332 can be connectedthrough the via 334. A dielectric layer 220 can be stacked in betweenthe first metal layer 210-1 and the second metal layer 210-2. Thedielectric layer 220 can be distinguished into the first dielectriclayer 220 a and the second dielectric layer 220 b according to theirformation time. Here, the metal plate 332 can be placed between thefirst dielectric layer 220 a and the second dielectric layer 220 b.

The first metal layer 210-1, the second metal layer 210-2, the metalplate 332 and the via 334 can consist of a metal material (e.g. copper)capable of being provided with an electric power and transferred to asignal.

The first dielectric layer 220 a and the second dielectric layer 220 bcan consist of the same dielectric material, but alternatively, thedielectric layer 220 a and 220 b can consist of materials havingdifferent dielectric constants from each other.

If the first meal layer 210-1 is a ground layer, the second metal layer210-2 is a power layer. Also, if the first metal 210-1 is the powerlayer, the second layer 210-2 is the ground layer. In other words, thefirst metal layer 210-1 and the second metal layer 210-2 can be each oneof the ground layer and the power layer, which are placed close to eachother, and the dielectric layer 220 can be placed between the groundlayer and the power layer.

Even though FIG. 7 illustrate the metal plate 332 having a regularsquare shape, the metal plate 332 can have various other shapes such aspolygon, circles and ellipses.

The metal plate 332 can be formed with a hole 320. The via 334 can beplaced in the hole 320. The via 334 and the metal plate 332 can beconnected through a metal line 310 (refer to FIG. 7 and FIG. 8).

The method of forming the via 334 will be described as follows.

The first metal layer 210-1, the first dielectric layer 220 a and themetal plate 332 can be successively stacked in. A via land 340 can beformed at a position in the metal plate 332. Here, the position of themetal plate 332 can be the position in which the via 334 is desired tobe formed for the electrical connection to the first metal layer 210-1.The via land 340, which is to reduce the position error in the drillingprocess for forming the via 334, can be formed more largely than thesectional area size of the via 334.

The via land 340 can be formed in the hole 320 penetrating the metalplate 332. The via land 340 and the hole 320 can formed by the typicalprocesses of manufacturing the printed circuit board such as masking,exposure, etching and development before the metal plate 332 is formedor simultaneously when the metal plate 332 is formed.

Also, the via 334 penetrating the via land 340 and the first dielectriclayer 220 can be formed through the drilling process. Alternatively, thevia 334 penetrating the via land 340, the first dielectric layer 220 andthe first metal layer 210-1 can be formed the drilling process.

After the via 334 is formed, the plating process can be performed toallow a plating layer to be formed on the inside wall of the via 334 inorder to electrically connect the first metal layer 210-1 to the vialand 340. According to the plating process, a plating layer can beformed on the inside wall of the via 334 excluding the center part amongthe inside part of the via 334. Alternatively, the entire inside part ofthe via 334 can be completely filled. In case that the inside part ofthe via 334 has an empty center part, the empty center part can befilled with the dielectric material or air. Since the formation of thevia 334 is evident to any person of ordinary skill in the art, thepertinent detailed description will be omitted.

The via 334 can have one end part 334 b, which is connected to the firstmetal layer 210-1, and the other end part 334 a, which is connected tothe via land 340 placed in the hole 320 that is formed in the metalplate 332. The metal line 310 can have one end part 310 a, which isconnected to the via land 340, and the other end part, which isconnected to the metal plate 332.

The metal line 310 can be placed on the same planar surface as the metalplate 332. Also, the metal line 310 and the metal plate 332 can besimultaneously formed at the same step among the processes ofmanufacturing the electromagnetic bandgap structure 330.

As shown in FIG. 7 and FIG. 8, the metal line 310 can have the shape ofstraight line. Alternatively, the metal line 310 can have various othershapes such as a curve and a spiral.

The hole 320 can be away from the via land 340 that is connected to theother end part 334 a of the via 334 at a predetermined interval. Also,the inside wall of the hole 320 can be away from the parts of the metalline 320 excluding a part connected to the metal plate 332 at apredetermined interval.

At least one mushroom type structure 330 including the metal plate 332and the via 334 can be formed between the first metal layer 210-1 andthe second metal layer 210-2.

The metal plate 332 of the mushroom type structure 330 can be arrangedon the same planar surface or the different planar surface between thefirst metal layer 210-1 and the second metal layer 210-2. Also, eventhough FIG. 6 illustrates that the via 334 of the mushroom typestructure 330 is connected to the first metal layer 210-1, the via 334of the mushroom type structure 330 can be connected to the second metallayer 210-2.

Also, a plurality of mushroom type structures 330 can be connected tothe first metal layer 210-1 or the second metal layer 210-2 through thevia 334. Alternatively, some of the mushroom type structures 330 can beconnected to the first metal layer 210-1, and the others can beconnected to the second layer 210-2.

FIG. 7 illustrates the structure in which the mushroom type structures330 is away from each other at predetermined intervals and be repeatedlyarranged. The repeated formation of the mushroom type structures 330 canmake it possible to block a signal having a frequency band correspondingto an operation frequency band of an analog circuit (e.g. an RF circuit)among an electromagnetic wave proceeding from a digital circuit to theanalog circuit.

By forming the structure of the metal plate 332 connected to the via 334in the mushroom type structure 330 as shown in FIG. 6 through FIG. 8,the capacitance value C_(E) between the metal plate 332 and the secondmetal layer 210-2 can be reduced negligibly. Also, the inductance valueL_(E) to be connected in series between the metal plate 332 and thefirst metal layer 210-1 in accordance with the via 334 can be acquiredenough.

Accordingly, in spite of the miniaturized size of the mushroom typestructure 330, the bandgap frequency band can be lowered instead ofbeing raised. The bandgap frequency can refer to the frequency preventedfrom being transferred among the frequencies transferred from a side toanother side. In the embodiment of the present invention, the bandgapfrequency band can correspond to 0.8 to 2.0 GHz, which is the operationfrequency band in the RF circuit of the mobile communication terminal.

FIG. 9 is graphs showing results that are computer-simulated by usingelectromagnetic bandgap structures in accordance with a conventional artand an embodiment of the present invention.

FIG. 9 illustrates the conventional electromagnetic bandgap structure(i.e. the metal plate 232) having the size of 49 mm²(7×7) (referring to910) and the conventional electromagnetic bandgap structure (i.e. themetal plate 232) having the size of 324 mm²(18×18) (referring to 920).

If the structure has the size of 49 mm²(7×7) (referring to 910), thefrequency having the noise level of (−) 50 dB or lower is 2.0 to 3.6GHz, and the bandgap frequency, which is the center frequency, can be2.8 GHz.

If the structure has the size of 324 mm²(18×18) (referring to 920), thefrequency having the noise level of (−) 50 dB or lower is 0.7 to 1.3GHz, and the bandgap frequency, which is the center frequency, can be1.0 GHz.

In other words, in accordance with the conventional electromagneticbandgap structure 200, if the bandgap frequency is placed in the bandbetween 0.8 and 1.0 GHz, which is the operation frequency of the RFcircuit used in the mobile communication terminal, it is necessary thatthe structure has the size of 324 mm²(18×18) (referring to 920).

However, in accordance with the electromagnetic structure 300 accordingto an embodiment of the present invention, if the structure has the sizeof 49 mm²(7×7) (referring to 930), the frequency having the noise levelof (−) 50 dB or lower can be 0.8 to 1.2 GHz, and the bandgap frequency,which is the center frequency, can be 1.0 GHz.

This can be charted as shown in the following table 1.

TABLE 1 Bandgap Noise frequency Structure size level Conventionalstructure 2.8 GHz    49 mm² (7 × 7) (−) 50 dB (shown in FIG. 4) 1 GHz324 mm² (18 × 18) (−) 50 dB Structure of invention 1 GHz  49 mm² (7 × 7)(−) 50 dB (shown in FIG. 8)

In other words, it can be recognized that the electromagnetic bandgapstructure 300 accordance with an embodiment of the present invention isable to not only have the same bandgap frequency as the conventionalelectromagnetic bandgap structure 200 but also lower the structure sizeby ⅙ or more (i.e. 324 mm²→49 mm²).

Also, in the case of having the same structure size, it can berecognized that the bandgap frequency is lowered by ⅓ or more (i.e. 2.8GHz→1 GHz).

FIG. 10 is a 3-D perspective view showing an electromagnetic bandgapstructure in accordance with another embodiment of the presentinvention, and FIG. 11 is a plan view showing the structure in which aplurality of metal plates of the electromagnetic bandgap structure shownin FIG. 10 are arranged. FIG. 12 is a 3-D perspective view showing anelectromagnetic bandgap structure in accordance with another embodimentof the present invention, and FIG. 13 is a plan view showing thestructure in which a plurality of metal plates of the electromagneticbandgap structure shown in FIG. 12 are arranged.

The electromagnetic bandgap structure 400 can include a first metallayer 410, a second metal layer 420, a first dielectric layer 430 a, asecond dielectric layer 430 b, a first metal plate 440 a, a second metalplate 440 b and a via 450.

A mushroom type structure 460 can be configured to include the firstmetal plate 440 a having a certain size, a second metal plate 440 b,accommodated into a hole 445 which is formed in the first metal plate440 a, and the via 450 having one end part which is connected to thefirst metal layer 410 and the other end part which is connected to thesecond metal plate 440 b. The first metal plate 440 a and the secondmetal plate 440 b can be placed at the same planar surface. An insidewall of the hole 445 of the first metal plate 440 a and an outside wallof the edge part of the second metal plate 440 b can be away from eachother. Accordingly, the inside wall of the first metal plate 440 a andthe outside wall of the edge part of the second metal plate 440 b can beelectrically connected to each other through a metal line 442.

The first dielectric layer 430 a can be stacked in the first metal layer410, and the first metal plate 440 a and the second metal plate 440 bcan be stacked in the first dielectric layer 430 a. The seconddielectric layer 430 b can be stacked in the first metal plate 440 a,the second metal plate 440 b and the first dielectric layer 430 a. Thedielectric layer 430 can be distinguished into the first dielectriclayer 430 a and the second dielectric layer 430 b according to theirformation time. Here, the first metal plate 440 a and the second metalplate 440 b can be placed between the first dielectric layer 430 a andthe second dielectric layer 430 b.

The first metal layer 410, the second metal layer 420, the first metalplate 440 a, the second metal plate 440 b and the via 450 can consist ofa metal material (e.g. copper) capable of being provided with anelectric power and transferred to a signal.

The first dielectric layer 430 a and the second dielectric layer 430 bcan consist of the same dielectric material, but alternatively, thedielectric layer 430 a and 430 b can consist of materials havingdifferent dielectric constants from each other.

If the first meal layer 410 is a ground layer, the second metal layer420 is a power layer. Also, if the first metal 410 is the power layer,the second layer 420 is the ground layer. In other words, the firstmetal layer 410 and the second metal layer 420 can be each one of theground layer and the power layer, which are placed close to each other,and the dielectric layer 430 can be placed between the ground layer andthe power layer.

Even though the first metal plate 440 a having a regular square shape isillustrated, the first metal plate 440 a can have various other shapessuch as polygon, circles and ellipses. Similarly, although the secondmetal plate 440 b having a regular square shape is illustrated, thesecond metal plate 440 b can have various other shapes such as polygon,circles and ellipses.

The method of forming the electromagnetic bandgap structure 400 will bedescribed as follows.

The first metal layer 410 and the first dielectric layer 430 a can bestacked in.

Then, the via 450 penetrating the first dielectric layer 430 a can beformed through the drilling process in order to allow the second metalplate 440 b which is supposed to be stacked in the first dielectriclayer 430 a to be electrically connected to the first metal layer 410.

After the via 450 is formed, the plating process can be performed toallow a plating layer to be formed on an inside wall of the via 450 inorder to electrically connect the first metal layer 410 to the secondmetal plate 440 b. According to the plating process, a plating layer canbe formed on the inside wall of the via 450 excluding the center partamong the inside part of the via 450. Alternatively, the entire insidepart of the via 450 can be completely filled. In case that the insidepart of the via 450 has an empty center part, the empty center part canbe filled with the dielectric material or air. Since the formation ofthe via 450 is evident to any person of ordinary skill in the art, thepertinent detailed description will be omitted.

In an embodiment of the present invention, after a metal layer isstacked in the first dielectric layer 430 a, the first metal plate 440a, the second metal plate 440 b and the metal line 442 can be formedthrough a patterning process. Here, the detailed description related tothe patterning process, which can use masking, exposure, etching anddevelopment that are typically used to form a circuit pattern in theprinted circuit board, will be omitted.

The electromagnetic bandgap structure 400 can be formed by successivelystacking the second dielectric layer 430 b and the second metal layer420.

At least one mushroom type structure 460 including the first metal plate440 a, the second metal plate 440 b, the metal line 442 and the via 450can be formed between the first metal layer 410 and the second metallayer 420. A plurality of mushroom type structure 460 can have metalplates arranged on the same planar surface or the different planarsurface. Also, the via 450 of the mushroom type structure 460 can facethe first metal layer 410. Alternatively, the via 450 of the mushroomtype structure 460 can face the second metal layer 420.

In the plurality of mushroom type structures 460, all of the vias 450can face the first metal layer 410 or the second metal layer 420.Alternatively, the vias 450 of some mushroom type structures 460 canface the first metal layer 410, and the vias 450 of the other mushroomtype structures 460 can face the second metal layer 420.

The metal line 442 can have a straight-line shape (refer to FIG. 10) ora spiral shape (refer to FIG. 12). Alternatively, the metal line 442 canhave various shapes. Any shapes having one end part, connected to thefirst metal plate 440 a, and the other end part, connected to the secondmetal plate 440 b, can be applied to the present invention.

FIG. 11 or FIG. 13 illustrates that the mushroom type structures 460 isaway from each other at predetermined intervals and be repeatedlyarranged. The repeated formation of the mushroom type structures 460 canmake it possible to block a signal having a frequency band correspondingto an operation frequency band of an analog circuit (e.g. an RF circuit)among an electromagnetic wave proceeding from a digital circuit to theanalog circuit.

The mushroom type structures 460 can be not only miniaturized but alsohave a lower bandgap frequency by connecting the second metal plate 440b connected to the via 450 to the first metal plate 440 a by use of themetal line 442 in the mushroom type structures 460.

FIG. 14 is graphs showing results that are computer-simulated by usingelectromagnetic bandgap structures in accordance with a conventional artand another embodiment of the present invention.

FIG. 14 illustrates the conventional electromagnetic bandgap structure(i.e. the metal plate 232) having the size of 4 mm²(2×2) (referring to1410) and the conventional electromagnetic bandgap structure (i.e. themetal plate 232) having the size of 64 mm²(8×8) (referring to 1420).

If the structure has the size of 4 mm²(2×2) (referring to 1410), thefrequency having the noise level of (−) 50 dB or lower is 2.0 to 5.5 GHzor higher.

If the structure has the size of 64 mm²(2×2) (referring to 1410), thefrequency having the noise level of (−) 50 dB or lower is 2.0 to 1.5 to1.8 GHz, and the frequency having the lowest noise level is 1.7 GHz.

In other words, in accordance with the conventional electromagneticbandgap structure 200, if the bandgap frequency is placed in the bandbetween 0.8 and 1.7 GHz, which is the operation frequency of the RFcircuit used in the mobile communication terminal, it is necessary thatthe structure has the size of 64 mm²(8×8) (referring to 1420).

However, in accordance with the electromagnetic structure 400 accordingto another embodiment of the present invention, if the structure has thesize of 4 mm²(2×2) (referring to 1430), the frequency having the noiselevel of (−) 50 dB or lower can be 1.2 to 3.2 GHz, and the frequencyhaving the lowest noise level can be 1.7 GHz.

This can be charted as shown in the following table 2.

TABLE 2 Bandgap frequency Structure size Noise level Conventionalstructure 7.5 GHz  4 mm² (7 × 7) (−) 50 dB 1.7 GHz 64 mm² (18 × 18) (−)50 dB Structure of invention 1.7 GHz  4 mm² (7 × 7) (−) 50 dB

In other words, it can be recognized that the electromagnetic bandgapstructure 400 accordance with another embodiment of the presentinvention is able to not only have the same bandgap frequency as theconventional electromagnetic bandgap structure 200 but also lower thestructure size by 1/16 or more (i.e. 64 mm²→4 mm²).

Also, in the case of having the same structure size, it can berecognized that the bandgap frequency is lowered by ¼ or more (i.e. 7.5GHz→1.7 GHz).

The printed circuit board of the present invention can include an analogcircuit and a digital circuit. The analog circuit can be the RF circuitsuch as an antenna receiving a wireless signal from an outside.

In the printed circuit board, the electromagnetic bandgap structures 300and 400 in accordance with an embodiment (refer to FIG. 6 through FIG.8) and another embodiment (refer to FIG. 10 through FIG. 13) of thepresent invention can be arranged between the analog circuit and thedigital circuit. In other words, the electromagnetic bandgap structure300 or 400 can be arranged between the RF circuit 140 and the digitalcircuit 130 in the printed circuit board as shown in FIG. 1.

In the digital circuit 130, the electromagnetic bandgap structure 300 or400 can be arranged in order to allow an electromagnetic wavetransferred from the digital circuit 130 to the RF circuit 140 tonecessarily to pass through the electromagnetic bandgap structure 300 or400. In other words, the electromagnetic bandgap structure 300 or 400can be arranged in a closed curve shape about the RF circuit 140 or thedigital circuit 130.

Alternatively, the electromagnetic bandgap structure 300 or 400 can bearranged in a signal transferring path between the digital circuit andthe analog circuit.

Arranging the electromagnetic bandgap structure 300 or 400 inside theprinted circuit board having the analog circuit and the digital circuitthat are embodied together therein can make it possible to prevent anelectromagnetic wave having a certain frequency band (e.g. 0.8 to 2.0GHz) among the electromagnetic wave transferred from the digital circuitand the analog circuit from being transferred.

In other words, in spite of the miniaturized size of the structure, theforgoing mixed signal problem can be solved by preventing anelectromagnetic wave having a particular frequency band corresponding tonoise from being transferred in the RF circuit 140.

Hitherto, although some embodiments of the present invention have beenshown and described for the above-described objects, it will beappreciated by any person of ordinary skill in the art that a largenumber of modifications, permutations and additions are possible withinthe principles and spirit of the invention, the scope of which shall bedefined by the appended claims and their equivalents.

1. An electromagnetic bandgap structure in which a first metal layer, afirst dielectric layer, a second dielectric layer and a second metallayer are stacked, the structure comprising: a first metal plate, formedbetween the first dielectric layer and the second dielectric layer; asecond metal plate, formed on a same planar surface as the first metalplate, accommodated into a hole which is formed in the first metal plateand electrically connected to the first metal plate through a metalline; and a via, connecting the second metal plate to any one of thefirst metal layer and the second metal layer.
 2. The electromagneticbandgap structure of claim 1, wherein the metal line is formed on a sameplanar surface as the first metal plate and the second metal plate. 3.The electromagnetic bandgap structure of claim 1, wherein the firstmetal plate is away from the second metal plate at a predeterminedinterval.
 4. The electromagnetic bandgap structure of claim 1, whereinthe metal line has a straight-line shape or a curved shape.
 5. Theelectromagnetic bandgap structure of claim 1, wherein the metal line hasa spiral shape enveloping the second metal plate.
 6. A printed circuitboard having an analog circuit and a digital circuit, the printedcircuit board in which an electromagnetic bandgap structure is disposedbetween the analog circuit and the digital circuit, the electromagneticbandgap structure comprising: a first metal plate, formed between thefirst dielectric layer and the second dielectric layer; a second metalplate, formed on a same planar surface as the first metal plate,accommodated into a hole which is formed in the first metal plate andelectrically connected to the first metal plate through a metal line;and a via, connecting the second metal plate to any one of the firstmetal layer and the second metal layer.
 7. The printed circuit board ofclaim 6, wherein the first metal layer is any one of a ground layer anda power layer, and the second metal layer is the other.
 8. The printedcircuit board of claim 6, wherein the analog circuit is an RF circuitincluding an antenna receiving a wireless signal from an outside.
 9. Theprinted circuit board of claim 6, wherein the metal line is formed on asame planar surface as the first metal plate and the second metal plate.10. The printed circuit board of claim 6, wherein the first metal plateis away from the second metal plate in a predetermined interval.
 11. Theprinted circuit board of claim 6, wherein the metal line has astraight-line shape or a curved shape.
 12. The printed circuit board ofclaim 6, wherein the metal line has a spiral shape enveloping the secondmetal plate.
 13. The printed circuit board of claim 6, wherein aplurality of electromagnetic bandgap structures are arranged between theanalog circuit and the digital circuit.
 14. An electromagnetic bandgapstructure, comprising: a first metal layer; a first dielectric layer,stacked in the first metal layer; a metal plate, stacked in the firstdielectric layer; a via, having one end part which is connected to thefirst metal layer; a second dielectric layer, stacked in the metal plateand the first dielectric layer; and a second metal layer, stacked in thesecond dielectric layer, whereas the other end part of the via isconnected to a via land which is placed in a hole formed in the metalplate, and the via land is connected to the metal plate through a metalline.
 15. The electromagnetic bandgap structure of claim 14, the metalline has a straight-line shape, a curved shape or a spiral shape.
 16. Aprinted circuit board having an analog circuit and a digital circuit,the printed circuit board in which an electromagnetic bandgap structureis disposed between the analog circuit and the digital circuit, theelectromagnetic bandgap structure comprising: a first metal layer; afirst dielectric layer, stacked in the first metal layer; a metal plate,stacked in the first dielectric layer; a via, having one end part whichis connected to the first metal layer; a second dielectric layer,stacked in the metal plate and the first dielectric layer; and a secondmetal layer, stacked in the second dielectric layer, whereas the otherend part of the via is connected to a via land which is placed in a holeformed in the metal plate, and the via land is connected to the metalplate through a metal line.
 17. The printed circuit board of claim 16,wherein the first metal layer is any one of a ground layer and a powerlayer, and the second metal layer is the other.
 18. The printed circuitboard of claim 16, wherein the analog circuit is an RF circuit includingan antenna receiving a wireless signal from an outside
 19. The printedcircuit board of claim 16, wherein the metal line has a straight-lineshape, a curved shape or a spiral shape.